1. Field of the Invention
The invention relates to electrical switchboard apparatus and more particularly to switchboards having a main supply bus and a perpendicular distribution bus forming a part of such switchboard apparatus.
2. Description of the Prior Art
An electrical distribution switchboard distributes the main incoming power among various site functions such as heating, lighting, and air conditioning. It typically consists of a number of vertical cabinet sections containing circuit breakers for switching and protecting the various load circuits. Three-phase electrical power enters the switchboard via cable or bus duct which is then connected to a main bus running horizontally within the switchboard between the various sections. The main bus is connected to vertical, or riser, bus in each vertical cabinet section. Various circuit breakers stacked vertically in each section have their inputs connected to the vertical riser bus and their outputs connected to horizontal load side extensions which run toward the rear of the cabinet perpendicular to the main horizontal bus. Bus duct or cable is then attached to the load side extensions to permit the power to exit the switchboard and flow to the load (air conditioning, lighting, motors, etc.).
The primary requirement for a switchboard is that it be safe and dependable. Other desirable characteristics include low cost in construction, installation, and maintenance. In addition, the switchboard should be of compact construction to reduce space requirements at the user location.
Under severe overcurrent conditions high electrodynamic forces are produced between the conductors of the bus system. Sufficient rigidity must therefore be provided to resist these forces and prevent movement of the bus system under these conditions.
It is also necessary to provide vertical riser bus conductors having ample current carrying capacity to supply the connected load circuits without overheating. Sufficient conductor cross sectional area and surface area must therefore be provided.
Circuit interrupters mounted in the switchboard are usually of the draw-out type, allowing them to be easily removed for testing or maintenance. Fixed sliding contact connectors are therefore provided in the switchboard to cooperate with movable sliding contact connectors on the circuit interrupters to facilitate insertion and removal. These insertion and removal operations produce wear upon the sliding contact connectors, and they eventually require replacement. It is desirable to provide means for replacement of the fixed connectors from the front of the switchboard without requiring access to the bus compartment.
Some or all of these features were provided for in prior art switchboards, such as disclosed in U.S. Pat. No. 3,780,355 (U.S. Cl. 317/120) issued Dec. 18, 1973 to John G. Salvati et al. It would be desirable, however, to provide a switchboard satisfying the above requirements at lower cost with more convenient assembly procedures.